It is known that dissimilar metal couples may exhibit extreme galvanic corrosion when a significant electromotive force difference exists between the two metals, in an electrically conductive environment, such as salt water.
Heretofore it was known to provide corrosion preventive grease formulations for protection of specific metals in corrosive atmospheres. Such typical greases are disclosed in U.S. Pat. Nos. 3,981,810; 3,850,823; 3,816,310; 3,781,218; and 3,623,982.
In certain industries greases based on petroleum oil compositions were not entirely satisfactory and synthetic oils were employed. Such synthetic oils however induced corrosion and certain treatment was made to the synthetic oils to prevent corrosion, as disclosed in U.S. Pat. No. 3,793,197 granted Feb. 19, 1974.
U.S. Pat. No. 3,383,328, granted May 14, 1968, to Baker and Leach, refers to corrosion protection of metal couples, specifically stainless steel to aluminum. The active ingredient disclosed is a reaction product of an amine and unsaturated fatty acid.
Many industries rely on grease compositions based on various types of petroleum or snythetic components and various types of soap or non-soap thickeners. Such compositions may include additives to achieve certain specific properties such as rust protection, and the primary purpose of such grease compositions is generally for use as a lubricant. However, such grease formulations have not been known to give corrosion protection between dissimilar metals such as bronze and aluminum.
Many industries however continue to rely on greases based on petroleum oil compositions which generally prove satisfactory as lubricants except where dissimilar mating metals were used. In such cases these greases did not avoid the galvanic corrosion caused by the dissimilar metals when water is present.
A specific problem area is the rapid galvanic corrosion that takes place between a metal coupling of bronze and aluminum, in the presence of a corrosive atmosphere, as is used in some types of fire-fighting equipment. For obvious reasons threaded connections between the bronze and aluminum components must be readily moveable, generally manually moveable without any specific tools. Extreme galvanic corrosion can prevent adjustment of the fire hose nozzle water flow or disassembly of the threaded parts.
Now, there is provided by the present invention a dissimilar metal coupling with a petroleum oil base grease composition which prevents the galvanic corrosion heretofore encountered.
More particularly by the present invention a coupling is made available wherein the bronze and aluminum mating parts such as in fire-fighting equipment are not subject to galvanic corrosion.
The aforesaid as well as other objects and advantages will become apparent from a reading of the following specification and the adjoined claims: